What is the most effective way to learn natural language processing online?
I think you could learn NLP ,by taking this course https://see.stanford.edu/Course/CS224N
Natural Language Processing - Stanford University | Coursera and try your best with the homework.

To further study, you could learn some deep learning algorithms like RNN. And of course, it’s better that you will be able to learn more a lot from university professors with minimal time period.

Hope it can help you.